Lennard-Jones流体固液相变的分子动力学模拟

采用等温等容分子动力学模拟方法，研究了ＬｅｎｎａｒｄＪｏｎｅｓ流体从固相到液相体系结构和性质的变化。均方位移，径向分布函数，平动序参数等结构和性质的模拟表明体系经历了固液相变。在对比密度为０．８４，０．８６，０．８８和０．９时，体系熔点分别为０．６６～０．６７，０．７１～０．７２，０．８２～０．８３和０．９０～０．９１。     

Prediction of thermodynamic properties for fluid nitrogen with molecular dynamics simulations

Molecular dynamics simulation results in the isochoric isothermal ensemble are reported for a two-center Lennard Jones model of fluid nitrogen characterized by the fixed molecular elongationL = 1 = 0.3292, New values of and were determined by fitting the vapor pressure and the saturated liquid density of the model to experimental data at 94,67 K. The required vapor liquid equilibrium data of the model were taken from a study using the NpT + test particle method. The resulting values are k = 36.32013 K (36.673 K) and = 0.32973 nm (0.33073 nm), with values in parentheses being those obtained previously from a Weeks Chandler Andersen-type perturbation theory. Then pressures and internal energies were calculated by molecular simulations for 110 state points in the temperature range from 72 to 330 K and for densities up to 35 mol · L¹. Comparison of the predictions based on the new parameters with the empirical equation of state of Jacobsen et al. shows good to excellent agreement except in the near-critical region. Moreover. for almost all state points the new parameters yield an improvement over old ones from perturbation theory.     

Molecular dynamics simulation of self‐diffusion coefficient and its relation with temperature using simple Lennard‐Jones potential

The diffusion coefficient is indispensable to chemical engineering design and research. In practical engineering and research, there is still a great lack of available data. Therefore, methods need to be developed to solve this problem. In this paper, a molecular dynamics simulation method is used to predict the self‐diffusion coefficient for a simple fluid by using the Green– Kubo relation (VACF) and the Einstein relation (MSD). The simulation results are in good agreement with experimental findings except for an error of about 10%. The algorithm average of the two methods (AV) reduces the error to 7%. The relationship of the diffusion coefficient with temperature has also been simulated. According to the simulation data, whose correlation is all above 0.99, the diffusion coefficient agrees well with temperature following the Arrenhius relationship. Activation energy for self‐diffusion has been calculated and the result were 1258(VACF), 1272(MSD), and 1265(AV) J/mol separately. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(2): 86–93, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20191     

微机械纳米接触原子层数的连续方法研究

为解决微机械中“微碰撞”、“纳米接触”问题 ,建立了纳米接触的刚性球 -面模型。根据 Ham aker三个假设和L ennard- Jones势 ,利用连续方法推导出球同平面第一和第 N层原子之间的作用力表达式 ,仿真出粘着力同原子层之间的关系 ,得出影响纳米接触的主要原子为接触区域少数几层原子的结论 ,从而为纳米接触、纳米摩擦的进一步研究提供理论基础     

加压下纯流体表面张力的统计热力学模型

从Ｋｉｒｋｗｏｏｄ－Ｂｕｆｆ理论出发，引入Ｇｕｂｂｉｎｓ的Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ模型流体的径向分布函数表达式，建立了一个三参数分子热力学模型，可以准确计算加压下纯流体的表面张力。对２２个纯组分流体的表面张力进行了关联，温度从常温到临界点，压力从常压到几十个大气压，计算的平均标准差为０．６０５５ｍＮ／ｍ，精度令人满意。     

Modelling of particle resuspension by a turbulent airflow and the role of particle size,surface roughness and electric charge

A resuspension model based on the Lennard–Jones intermolecular potential is applied to a monolayer deposit of spherical particles. The model considers the interactions between a particle and a surface under the influence of an external turbulent airflow. The particle–surface interaction was modelled with and without particle deformation due to elastic flattening. The resuspension rate was calculated by a kinetic force-balance approach whereby particle detachment occurs when the instantaneous joint contribution of the lift and drag forces exceeds the total adhesive force of the particle–surface system. Enhanced aerodynamic particle removal driven by the moment of the lift and drag forces was determined. Model predictions suggest that inclusion of the moment of the aerodynamic forces provides a suitable model for particle detachment (initiated by rolling). The importance of elastic deformation was found to depend on adhesive forces, characteristics of the substrate surface (surface roughness) and particle size. The model was applied to a number of laboratory experiments. For one set of experiments, we identified two resuspension regimes depending on whether small non-deformable or large deformable (equivalently, strongly or weakly bound) particles resuspended at high or low friction velocities. A modified model incorporating the effect of particle charge is also presented. Results indicate that particle resuspension is possible even when electrostatic forces are present, but the resuspension rate decreases considerably, depending on particle size, particle charge and surface roughness.     

A new concept for augmented van der Waals equations of state

A novel approach to perturbed equations of state for simple fluids is presented and its advantages over the traditional perturbed hard sphere equations are demonstrated by its application to several model fluids. The approach is based on a short range Yukawa reference which incorporates, in addition to repulsive interactions, also attractive interactions at short separations. The considered models of common interest are the Sutherland, Lennard-Jones, and EXP6 fluids. It is shown that using the proposed approach the reference system captures a good deal of properties of the studied fluids and that an accurate equation of state can be obtained using only the crude mean field (augmented van der Waals) approach.     

Equilibrium,interfacial and transport properties of n-alkanes: Towards the simplest coarse grained molecular model

In this work, using molecular dynamics simulations, we have investigated how simple could be a coarse grained molecular model yielding simultaneously equilibrium densities, surface tensions and transport properties of some n-alkanes (from methane to n-decane) along the vapour–liquid equilibrium curve. For that purpose, as an initial model, the fully flexible Lennard–Jones Chain (3 “molecular” parameters) model has been chosen. Using this simple molecular model, good results have been obtained on equilibrium properties of all tested n-alkanes despite a systematic slight overestimation of critical temperatures, critical pressures and surface tensions. In addition, concerning transport properties, good results have been obtained for methane and n-butane except for thermal conductivity in the gas state. For n-heptane and n-decane it has been found that thermal conductivity is systematically underestimated while viscosity is well estimated except at low temperatures. Concerning thermal conductivity, this misevaluation can be corrected if the zero-density thermal conductivity is known. Concerning shear viscosity, it is found that an additional “rigidity” fourth parameter is required to improve the results when dealing with the longest chains at the lowest temperatures.     

Droplets sliding over shearing surfaces studied by molecular dynamics

Through molecular dynamics, the sliding motion of a liquid drop embedded in another liquid over a substrate as a result of a shear flow is studied. The two immiscible Lennard‐Jones liquids have the same density and viscosity. The system is isothermal. Viscosity, surface tension, and static contact angles follow from calibration simulations. Sliding speeds and drop deformations (in terms of dynamic contact angles) are determined as a function of the shear rate. The latter is nondimensionalized as a capillary number (Ca) that has been varied in the range 0.02–0.64. For Ca up to 0.32, sliding speeds are approximately linear in Ca. For larger Ca, very strong droplet deformations are observed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4020–4027, 2015